1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method for forming images.
2. Description of the Related Art
In printers, faxes, and copiers employing an electrophotographic method, it is difficult to reproduce a highlighted portion of an image due to data loss caused by quantization of image data or the lack of toner attraction force that is a problem specific to such an electrophotographic method.
A portion having a pixel density that is 15 percent or less of the pixel density of a solid black portion will be hereinafter referred to as the most highlighted portion.
It is possible to solve the lack of toner attraction force by changing, for example, a transfer current process in an electrophotographic apparatus.
However, a so-called fog phenomenon in which toner is supplied to a portion requiring no toner on a sheet sometimes occurs.
Accordingly, an image processing method of forming an image without loss of data at the time of quantization of original image data and an image processing method of forming an image with sufficiently large toner attraction force between toner particles or between each toner particle and a photosensitive drum without dispersion of toner have been proposed.
Japanese Patent Laid-Open No. 5-95474 discloses a technique for binarizing image data while maintaining the density levels of pixels near a pixel of interest on an image at the time of quantization of the image data.
Using this technique, toner can be intensively supplied while minimizing loss of original image data of a highlighted portion.
Thus, in order to improve the roughness of an image due to binarization of image data, a method of converting image data into multi-valued image data at the time of quantization of the image data has come into general use.
However, even if the above-described method is used, the most highlighted portion of an original image is reproduced with a small amount of toner.
Accordingly, the attraction force between toner particles or between each toner particle and a photosensitive drum may not become sufficiently large, and a toner image may not be developed on a photosensitive drum.
Furthermore, a toner image on a photosensitive drum may not be transferred to a sheet, and the most highlighted portion of an image may not be reproduced.
Still furthermore, the efficiency of transferring toner to a sheet may be changed in accordance with a print environment or the endurance of a printer, and the most highlighted portion of an image may not be reproduced.